1. Field of the Invention
This invention relates to the field of protective and/or decorative surface treatment of articles, particularly metals and the like, to novel derivatives of polyphenol compounds useful in the treatment of the surface of various types, to surface treatment solutions or dispersions containing these novel polyphenol derivatives, and to methods of using these solutions or dispersions, particularly to treatments for improving the heat resistance of chromate conversion coatings on aluminum and to treatments for improving the rinsability of plastic and painted surfaces.
2. Statement of Related Art
The need for applying protective coatings to metal surfaces for improved corrosion resistance and paint adhesion characteristics is well known in the metal finishing art as well as in other metal arts. Traditionally, metal surfaces are treated with chemicals which form a metal phosphate and/or metal oxide conversion coating on the metal surface to improve the corrosion resistance and paint adhesion thereof. The conversion coated metal surfaces are also generally rinsed or post-treated with a solution containing a hexavalent chromium compound for even greater corrosion resistance and paint adhesion.
Because of the toxic nature of hexavalent chromium, expensive wastewater treatment equipment must be employed to remove the residual chromates from plant effluent to comply with environmental regulations and to improve the quality of rivers, streams, and drinking water sources. Hence, although the corrosion resistance and paint adhesion characteristics of conversion coated metal surfaces can be enhanced by an after-treatment solution containing hexavalent chromium, these environmental disadvantages have led in recent years to much research and development in an effort to uncover effective alternatives to the use of post-treatment solutions containing hexavalent chromium. One alternative to the use of hexavalent chromium involves the use of derivatives of polyphenol compounds such as poly-vinyl phenol. Suitable derivatives and suitable treatment solutions are disclosed in earlier U.S. Pat. Nos. 4,517,028 of May 14, 1985, 4,433,015 of Feb. 21, 1984, and 4,376,000 of Mar. 8, 1983 to Lindert and 4,457,790 of, Jul. 3, 1984 to Lindert, et al.; all of which, to the extent not inconsistent with any explicit statement herein, are expressly incorporated herein by reference.
In the treatment of articles for subsequent painting or decorative coatings, including metals and plastics, the parts or articles are normally cleaned with conventional cleaner systems. Plastic and painted surfaces when cleaned with conventional, non-etching, acidic or alkaline cleaner systems, produce a hydrophobic, non-water wettable surface. This non-wettable surface is due to the hydrophobic nature of the surface being treated. As expressed by W. A. Zisman, "Relation of the Equilibrium Contact Angle to Liquid and Solid Constitution", in R. F. Gould (editor), Contact Angle, Wettability, and Adhesion (American Chemical Society, Washington, 1964):
[H]ard solids have surface free energies ranging from about 5000 to 500 ergs per sq. cm., the value being higher the greater the hardness and the higher the melting point. Examples are the ordinary metals, metal oxides, nitrides, and sulfides, silica, glass, ruby, and diamond. Soft organic solids have much lower melting points and the surface free energies are generally under 100 ergs per sq. cm. Examples are waxes, solid organic polymers, and in fact, most solid organic compounds. Solids having high specific surface free energies may be said to have "high-energy surfaces" and solids having low specific surface free energies have "low-energy surfaces." . . . PA1 Because of the comparatively low specific surface free energies of organic and most inorganic liquids, one would expect them to spread freely on solids of high surface energy, since there would result in a large decrease in the free energy of the system, and this is most often found to be true. But since the surface free energies of such liquids are comparable to those of low energy solids, among these liquids should be found those exhibiting nonspreading on low-energy solids.
As a result of this fundamental difference between metal and plastic or painted surfaces, even perfect cleanliness of the latter type of surfaces is not sufficient to assure ready wetting of the plastic and painted surfaces by water. Accordingly, one problem to be solved by the present invention is to provide a method for conferring on plastic and painted surfaces sufficient hydrophilicity to enable them to be rinsed with water without forming water breaks, while not damaging adhesion of subsequently applied coatings to the plastic and painted surfaces thus treated.